PROJECT SUMMARY/ABSTRACT Neuropathic pain is an incapacitating consequence of cancer treatment with cytotoxic chemotherapeutics, such as paclitaxel. The economic cost of chronic pain, including neuropathic pain as a large component, has been estimated to be over $500 billion in the US alone. Existing treatments are largely ineffective, and neuropathic pain is one of the most common reasons for reducing chemotherapy dosing. Neuropathic pain may be short term (acute neuropathic pain) or it may persist after multiple doses of chemotherapy (chronic neuropathic pain). Although mechanisms for pain associated with chemotherapeutic-induced peripheral neuropathy (CIPN) are not known, other forms of chronic neuropathic pain are often associated with an inflammatory process and purinergic signaling. Our group previously found that Pannexin 1 (Panx1) channels, which release ATP and other potentially pro-inflammatory metabolites, are required for development and maintenance of neuropathic pain after direct nerve injury. Thus, I hypothesize that Panx1 may also contribute to CIPN-associated pain. My exciting preliminary data from knockout mice reveal a unique role for Panx1 specifically in the transition from acute to chronic pain. Specifically, Panx1-deleted mice developed acute mechanical hypersensitivity after an initial bout of paclitaxel, but unlike wild type mice, the neuropathic pain was not maintained and resolved after a second bout of paclitaxel. In this proposal, I examine the cellular and mechanistic basis for this role of Panx1 using behavioral assays with paclitaxel-treated mice, along with electrophysiological and immunological characterization of sensory neurons and immune cells in dorsal root ganglion (DRG). In Aim 1, I use genetic and pharmacological tools, including global and cell-specific Panx1 knockout mice, to determine the contribution of Panx1 in hematopoietic cells to chronic neuropathic pain. The hypothesis driving Aim 2 is that Panx1 is necessary for the persistent inflammation of DRG after repeated bouts of paclitaxel. I use patch clamp electrophysiology, flow-cytometry, and immunohistochemistry to determine neuron excitability and inflammatory states of DRG during acute and chronic phase of neuropathic pain. Collectively, this proposal will provide new information regarding Panx1 involvement in chronic chemotherapy-induced neuropathic pain, and a rationale for considering Panx1 as a novel target for treating this debilitating side effect of life-saving cytotoxic chemotherapies.